Modern communications demand higher data rates and performance. Multi-input, multiple output (MIMO) antenna systems, also known as multiple-element antenna (MEA) systems, achieve greater spectral efficiency for allocated RF channel bandwidths. MIMO systems increase the spectral efficiency by utilizing space or antenna diversity at both the transmitter and the receiver.
Transmitters typically include fixed pulse-shaping filters such as, for example, raised root cosine (RRC) or finite impulse response (FIR) filters. Such filters are designed to meet the emission mask at the maximum output power and operate with the same sampling rate, word length and number of taps regardless of the amount of out-of-band suppression required for that power level. Thus, these filters operate at the maximum processing power at all times. Such systems consume more power than necessary to maintain a proper emission profile and to maintain reliable communications on the RF link to the receiver.
There is therefore a need for efficient transmitter filters for use in MIMO systems. More particularly, there is a need for reconfigurable digital filters for MIMO transmitters that reduce processing power and power dissipation for multiple MIMO streams.